1. Field of the Invention
This invention relates to the construction of composite beams in a composite steel deck floor system.
2. Description of the Prior Art
The utilization of composite action between a concrete floor slab and the floor supporting beam is well known in the art. To achieve the composite beam action, it is required to install a shear transferring device such that a compressive bending force can be developed within the cured concrete slab. This type of design is known as a composite beam design. If there is no shear transferring device provided, the floor supporting beam must be designed to resist the total imposed load and is known as a non-composite beam design. It is well known in the art that the beam strength and stiffness are greatly increased in a composite beam design as compared to a non-composite beam design. Therefore, the composite beam design has been continuously gaining popularity in the building industry. Shear studs are commonly used in the composite beam design and are installed in the following procedures. The first step is to secure the steel decks to the supporting beams. The second step is to weld the shear studs at the valleys of the steel deck profile through the steel deck onto the top flange of the supporting beam. The third step is to place the concrete shrinkage control wire mesh at 1 inch (25.4 mm) below the finished concrete slab. The fourth step is to pour and to finish the concrete slab.
In the selection of the beam size in a composite beam design, the following two factors must be considered. First, the non-composite strength of the beam must be adequate to resist the dead weight of the floor and the construction loads. Second, upon curing of the floor slab, the composite strength of the composite beam must be adequate to resist the total imposed loads including the dead load and the design live load on the floor.
The drawbacks of the prior art composite beam design include the following items.
1. In most cases, the beam size is governed by the required non-composite beam strength during the erection period.
2. The efficiency of the shear stud is affected by the concrete rib geometry formed by the valleys of the steel deck profile. The wider the concrete rib, the higher the stud efficiency. The deeper the steel deck, the lower the stud efficiency. In some cases, only a partial composite design can be achieved due to a reduction of the stud efficiency induced by the steel deck profile or the available rib locations for stud welding.
3. The concrete shrinkage control mesh is supported by spaced apart plastic chairs. The plastic chairs can be easily knocked down during the concreting operation resulting in ineffective concrete shrinkage control due to mislocated wire mesh.